1. Field of the Invention
The present invention relates to non-invasive measurement of blood sugar levels for measuring glucose concentration in a living body without blood sampling, and an optical measurement apparatus suitable for that purpose.
2. Background Art
Hilson et al. report facial and sublingual temperature changes in diabetics following intravenous glucose injection (Non-Patent Document 1). Scott et al. discuss the issue of diabetics and thermoregulation (Non-Patent Document 2). Based on the knowledge gained from such researches, Cho et al. suggest a method and apparatus for determining blood glucose concentration by temperature measurement without requiring the collection of a blood sample (Patent Document 1 and 2).
Various other attempts have been made to determine glucose concentration without blood sampling. For example, a method has been suggested (Patent Document 3) whereby a measurement site is irradiated with near-infrared light of three wavelengths, and the intensity of traveled photon as well as the temperature of the living body is detected. A representative value of the second-order differentiated value of absorbance is then calculated, and the representative value is corrected in accordance with the difference of the living body temperature from a predetermined reference temperature. The blood sugar level corresponding to the thus corrected representative value is then determined. An apparatus is also provided (Patent Document 4) whereby a measurement site is heated or cooled while monitoring the living body temperature. The degree of attenuation of light based on light irradiation is measured at the moment of temperature change so that the glucose concentration responsible for the temperature-dependency of the degree of light attenuation can be measured. Further, an apparatus is reported (Patent Document 5) whereby an output ratio between reference light and the light transmitted by an irradiated sample is taken, and then the glucose concentration is calculated by a linear expression of the logarithm of the output ratio and the living body temperature. Another apparatus for measuring glucose concentration is provided (Patent Document No. 6) whereby the result of irradiating light from two light sources is detected by three infrared light detectors and also temperature is detected.    (Non-Patent Document 1) R. M. Hilson and T. D. R. Hockaday, “Facial and sublingual temperature changes following intravenous glucose injection in diabetics,” Diabete & Metabolisme, 8, pp.15-19: 1982    (Non-Patent Document 2) A. R. Scott, T. Bennett, I. A. MacDonald, “Diabetes mellitus and thermoregulation,” Can. J. Physiol. Pharmacol., 65, pp. 1365-1376: 1987    (Patent Document 1) U.S. Pat. No. 5,924,996    (Patent Document 2) U.S. Pat. No. 5,795,305    (Patent Document 3) JP Patent Publication (Kokai) No. 2000-258343 A    (Patent Document 4) JP Patent Publication (Kokai) No. 10-33512 A (1998)    (Patent Document 5) JP Patent Publication (Kokai) No. 10-108857 A (1998)    (Patent Document 6) U.S. Pat. No. 5,601,079